Exhaust apparatus and method

ABSTRACT

A rotary swaging method for the tapering of metal tubes is disclosed. The method comprises the use of a rotary swaging machine comprising a die comprising a die taper comprising a length of greater than about 12 inches, a diameter reduction of greater than about 30%, and/or a taper angle of less than about 12 degrees.

This claims priority to U.S. Provisional Application No. 60/947,116,filed on Jun. 29, 2007 and titled “EXHAUST APPARATUS AND METHOD” and itis herein incorporated by reference.

BACKGROUND

1. Technical Field

The present invention pertains to the field of metal working and theprocessing of tubular metal work pieces into long tapers. Morespecifically, the present disclosure relates to exhaust systems andmethods of manufacturing exhaust systems.

2. Background Information

Tapered tubular metal pieces, and tapered exhausts in particular, areconventionally made using either a rolling or forming process. Informing tapered metal tubes by the rolling process, sections are cutfrom flat sheet stock. The sections are then rolled into a desiredtaper, which is then closed with a seam weld running parallel to thelong axis of the taper. The weld is a point of weakness in the taperedpiece in that its raised surface makes it susceptible to mechanicaldamage. Furthermore, the weld is cosmetically undesirable in that itinterrupts the contour of the tapered piece. Prior to furtherprocessing, such as plating or finishing, the raised portion of the weldmust generally be ground flush with the surface of the piece. However,the reduction of the weld in order to improve the profile of the pieceweakens the weld, and thus the rolling method is limited by thisdisadvantage. The process is illustrated in FIGS. 1 and 2.

In forming tapered metal tubes by the forming process, a precut tube ismachined by press operations such as drawing or forging until the tubeis tapered to the desired diameter reduction. Cracking, flaking andstructural flaws are experienced at a high rate with these brute forcemethods, particularly at taper angles in excess of about 10 degrees.With regard to the forming process, profile design variations and taperlength are significantly limited due to inherent stamping processparameters, as illustrated in FIG. 5.

Both methods above have additional shortcomings in that they do notinclude within their scopes the preparation of modified tapers, inparticular, those having untapered tubular extensions of either end, andin particular, at the small-diameter end. If such extensions aredesired, it is necessary to follow the rolling and forming processesdescribed above with the connection of a flange to the small diameterend of the taper by an orbital weld around the diameter of a precutpiece of tubing. One example of such a connection is the connection of amotor cycle muffler to other engine exhaust piping.

Existing exhausts and methods of manufacturing such exhausts suffer froma number of drawbacks: In most cases all welds must be ground flush orotherwise controlled for desired cosmetics prior to further processingsuch as chrome plating. This additional weld preparation prior to chromeplating risks breakage at the weld site.

Tapered tubular metal work pieces are difficult to prepare by rotaryswaging because the process gives, in many instances, a worked producthaving negative structural and cosmetic characteristics such as flakingand cracking. Such characteristics give a product which is unusable. Theintended function of the pieces is to absorb acoustic energy from hotexhaust. The muffler can be heated to high temperatures before coolingto ambient temperature when engine operation ceases. Such heating andcooling cycles tend to exacerbate the negative characteristics impartedto the piece by present methods of metal tapering. Flaked sections soonseparate from the piece, leaving it vulnerable to longitudinal cracksand splits parallel to the long axis of the piece.

Furthermore, present methods of tapering metal work pieces render thepieces difficult to process further into desirable usable forms. Forinstance in making a muffler or an exhaust, present methods of formingthe taper do not permit the formation, during tapering, of an untaperedsection at the reduced bore end of the taper. As such a structure isdesirable in order to direct outgoing exhaust after it has passedthrough the muffler, methods in common use require that an untaperedpiece having the small end diameter of the taper be welded onto thetapered section in an end-to-end fashion. The additional weld, as withthe seam weld discussed above, may require further processing in orderto meet cosmetic objectives.

A method is disclosed for the rotary swaging of tapers having a taperangle of greater than about 10 degrees. Further disclosed is a methodfor the machining of such tapers from a single tubular work piece suchthat the taper has a length of constant diameter tubing extending fromthe small diameter end of the taper. Further disclosed is a machinedtaper produced by the method, having, optionally, a length of constantdiameter tubing extending from the small diameter end of the taper.Further disclosed is method which can be used to machine, in one pass, asubstantially flake-free and crack-free taper having a taper angle ofgreater than about 10 degrees, a diameter reduction of greater thanabout 20%, and a length of greater than about 12 inches; and a taperprepared by the method. Further disclosed is a method which can be usedto machine a tubular work piece, in one pass, from one length of tubing,into the foregoing taper, and additionally comprising a length ofconstant diameter tubing extending from the small diameter end of thetaper.

Rotary Swaging

Rotary swaging is generally performed with a rotary swaging apparatus.Such an apparatus generally comprises a circular outer race, a number ofcylindrical rollers in contact with the outer race, and a number of dieelements. The die elements are arranged about the work piece such thatby radially closing and releasing about the work piece, they shape thework piece by forcibly deforming it into a tapered tubular sectionhaving a profile which is ideally the profile of the die elements. Thepreferred method is known as “infeed swaging,” in which the work pieceis slowly advanced into the rhythmically opening and closing dieassembly. The profile of the die is tapered, and thus, as the work pieceis advanced into the die, the diameter of the tubular section at anypoint on the work piece which has entered the die is being continuallydecreased. In some cases, it is desirable to fabricate a tapered piecehaving a section of small diameter tubing extending from the smalldiameter end of the taper. This is accomplished by feeding the workpiece into the machine until it exits from the small diameter end of thetapered die. The extruded section is no longer in contact with the die,and will undergo no further reduction in diameter.

The die elements are constrained in their motion by wedge pieces whichfit between the die elements. The wedge elements prevent the dieelements from moving circumferentially with respect to each other, butallow the elements to move radially with respect to each other. The dieelements and the wedge elements together form a generally cylindricalassembly called the die assembly. The die assembly lies within acircular outer race. Between the inner surface of the outer race and theouter cylindrical surface of the die assembly lie evenly spacedcylindrical rollers. The rollers permit the die assembly to turn insidea stationary outer race, or the outer race to turn outside a stationarydie assembly.

The radial motion of the die elements is caused by the rollers, andoccurs when the die assembly moves with respect to the outer race. Whenthe die elements are at their most “open” position (i.e., they havepulled back from the work piece, and the work piece can be furtheradvanced into the die assembly, if desired) the outermost surface of thedie element extends above the outer surface of the die assembly. Whenthe die assembly moves with respect to the outer race, the rollersregularly contact the die elements and thrust them radially inward insimultaneous fashion as they roll between the die assembly and the outerrace. With each inward thrust, the die elements come together around thework piece, forcing the diameter of the work piece to be reduced alongthe area where it is in contact with the die elements. No “spillage”around the edges of the die elements occurs because the die assembly isgenerally rotated with respect to the work piece.

In general, the outer race and the die assembly rotate with respect toeach other. However, variations on the basic method allow for the outerrace to be rotated with the die assembly held static (the work piece isthen rotated as well); the die assembly rotated with the outer race heldstatic; or both allowed to rotate to some degree.

It has heretofore been thought that the method of rotary swaging couldnot be used for tapering operations involving large reductions indiameter, steep taper angles, or long tapers. For example, it is knownthat present methods of rotary swaging are not suitable for reductionsin diameter of greater than about 30% in a single pass in that they giveproducts with structural and cosmetic problems such as a flaking orcracking. Furthermore, present methods are substantially limited in thatthe angle of taper between the large and small diameters should notexceed 10-12 degrees. With current methods, the above problems areexacerbated if long tapers, such as greater than 12 inches, are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a muffler shell manufactured by rolling andwelding three separate components according to the prior art;

FIG. 2 is a side view of a muffler shell manufactured by rolling andwelding three separate components according to the prior art;

FIG. 3 is a side view of a press formed muffler shell according to theprior art;

FIG. 4 is a side view of a swaged muffler shell manufactured accordingto one aspect of the present invention; and

FIG. 5 is a side view of a swaged muffler shell manufactured accordingto one aspect of the present invention.

FIG. 6 is the schematic for a die capable of machining a taper having alength greater than 20 inches.

FIG. 7 is the schematic for a die capable of machining a taper havingboth convex and concave sections

FIG. 8 is the schematic for a die capable of machining a short taperhaving a taper angle of greater than 12 degrees.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

In general, the tubular metal work piece can be of a wide variety ofdimensions and comprised of a wide variety of materials. With respect tomaterials which can be used, carbon steel tubing, stainless steel tubingand aluminum tubing can be used, as well as other materials havingappropriate malleability and ductility characteristics. The gauge of thetubing is preferably in the range of from about 20 gauge (035) to 11gauge (125).

While medium diameter tubing may be machined according to the methodmore easily than tubing having very large or very small diameters, ingeneral, the method can be used to machine tubular work pieces of anydiameter, but preferably having a diameter of about 6 inches or less,and in preferred embodiments, a diameter in the range of from about 6inches to about 0.5 inches. Most preferred are embodiments in which thediameter is in the range of from about 6 inches to about 2 inches.

The die can be made of a wide variety of materials, subject to wearconsiderations. Generally, D2 High strength steel is preferred, butother materials having suitable wearing parameters can be used as well.For example, shock steel, such as 50 to 100, can be used. Othermaterials having appropriate hardness and wear characteristics includeother types of steel such as carbon steel.

The “taper angle” is the angle between the largest diameter and thesmallest diameter of the taper. Thus, looking at a die or a tapered workpiece in profile, the taper angle is the acute angle between the taperprofile line and the axis of the work piece. Because the swaging dieessentially imparts its own angle to the tubular work piece, in order toswage a taper having given characteristics such as taper angle, diameterreduction, and taper length, it is necessary to use a die having theproperties. As described above, and known in the art, the taper dies,when closed together about a work piece, define a tapered tube. Thus,when referring to a tube having a given taper, the die by which it wasformed must possess the same taper profile. As the work piece isadvanced into the die, the diameter profile of the tube is reduced toconform to the diameter profile of the die. Once the work piece has beenadvanced to such a degree that the end inserted initially reaches thesmall diameter end of the die, its diameter no longer changes uponfurther insertion of the work piece, and a length of tubing having thesmaller diameter is formed at the small diameter end of the taper. Thelength of the small diameter tubing increases as the work piece is fedinto the die assembly. It should be noted that as the piece of tubing isprocessed by the die, it is generally lengthened, and as the diameter ofa given section is reduced, the section generally undergoes an increasein wall thickness. Thus, the method of the present invention ischaracterized by the use of a die having a die taper angle of greaterthan about 10 degrees, and in additional embodiments, greater than about12, 14, 15, 16, 17 and 18 degrees. In general, the method can be used toachieve a taper having a taper angle of greater than about 10 degrees,and in additional embodiments, greater than about 12, 14, 15, 16, 17 and18 degrees. The method of the present invention also can be used to formextremely long tapers in one pass, for example, up to, including, andlonger than about 24 inches. In such cases, the taper angle may be evenless than about 10 degrees. Current methods require multiple passesthrough successively stretched tapers in order to form such long tapers.

The maximum taper length is dependent upon the length of the die taper.In general, a die taper of a given length can be used to form tapers ofthat length and shorter, with the shorter tapers formed by processing awork piece only partially. Fully processing a work piece (i.e., suchthat the inserted end reaches the small diameter end of the die taper)results in a taper having the length of the die taper. Further insertionof the work piece gives a length of tubing attached to the smalldiameter end of the taper, with the taper having the same length as thedie taper.

While the method of the present invention can be useful in thepreparation of tapers of a wide variety of dimensions, preferably thetaper has a length in the range of from about 10 to about 22 inches,more preferably in the range of from about 12 to about 20 inches, evenmore preferably in the range of from about 15 to about 20 inches.Furthermore, the method of the present invention can be used to form ataper having extensions of tubing from its small diameter end. Suchlengths of tubing can be as long as desired.

The method of the present invention can be used to prepare tapers havinga diameter reduction (between starting diameter and smallest finishingdiameter) of greater than 30%. Preferably, the diameter reduction isgreater than 10%, and more preferably it is greater than 20%.

The method of the present invention includes the use of a die with theabove angles, and it should be noted that in general, with an anglegiven above, the length of the die can vary greatly without departingfrom the scope of the present invention. Commonly desired taper lengths,such as those lengths which are useful in the motorcycle mufflerindustry, for example, in the range of from about 12 to about 24 inches,as well as lengths outside this range are within the scope of thepresent invention. It should be noted that not all combinations ofstarting diameter, taper length and taper angle are geometricallypossible, however, the method of the present invention enfolds theproduction of tapers having the above parameters, to the extent thatthey are geometrically sensible.

The present invention encompasses tapers which are not linear inprofile, i.e., tapers having convex profiles, concave profiles, orregions of both. Note the die given in example 7. The die taper profilebegins with a convex section followed by a short concave section (notethat the initial concavity is for the purpose of aiding the entrance ofthe work piece into the die assembly). In such cases the taper angle iscalculated as with straight tapers above using the initial and smallestdiameters.

While the inventive process disclosed herein relies on the use of aspecially dimensioned die, many of the details of the rotary swagingprocess are standard. The work piece can be fed into the rotary swagingmachine at wide variety of rates. Typical feed rates are in the range offrom about 0.062 to 0.500 inches per second. The velocity of the workpiece is in the range of from about 40 to 60 rpm, with the outer racevelocity generally faster. The holding clamp pressure on the work pieceis in the range of from about 20# to about 60#. Note that the clampreleases the work piece at intervals when the die pressure on the workpiece is at a minimum, and the work piece is rotated slightly, generallyby the die assembly. In general, the die assembly rotates at a higherrate relative to the work piece. The work piece is fed into the dieassembly at a hydraulic pressure in the range of from about 800 to1500#. The number of die elements (“pieces”) is preferably 2, 3 or 4.

The invention is described with reference to the drawings in which likeelements are referred to by like numerals. The relationship andfunctioning of the various elements of this invention are betterunderstood by the following detailed description. However, theembodiments of this invention as described below are by way of exampleonly, and the invention is not limited to the embodiments illustrated inthe drawings. It should also be understood that the drawings are not toscale and in certain instances details have been omitted, which are notnecessary for an understanding of the present invention.

FIGS. 4 and 5 illustrate a swaged muffler shell according to one aspectof the present invention. To manufacture a swaged muffler, precut tubepieces are rotary swaged to desired taper or profile. This method ismore flexible in that the degree of taper and taper length issignificantly more variable due to more flexible process parametersassociated with rotary swaging.

This method also allows rotary swaging of the taper or profile and theconnecting flange in one piece. This eliminates the need for secondarywelding operations and cosmetic grinding removal of weld prior to chromeplating. This method is significantly less costly and more cosmeticallydesirable. No welding required.

It is therefore intended that the foregoing detailed description beregarded as illustrative rather than limiting, and that it be understoodthat it is the following claims, including all equivalents, that areintended to define the spirit and scope of this invention.

EXAMPLES

The rotary swaging method of the present invention was used to create,in one pass, a taper having a taper angle which exceeded 12 degrees. Thetaper had a starting diameter of 4.500 inches, a small diameter of 2.008inches, and a taper length 2.768 inches. The small diameter end of thetaper had a length of straight tubing extending from it. The tube has astarting gauge of 14 gauge.

The swaging method of the present invention was used to create, in onepass, a taper having a 30% reduction in diameter. The taper had astarting diameter of 4.500 inches, a small diameter of 2.184 inches, anda taper length 5.504 inches. The reduction in diameter was 51.5%. Thesmall diameter end of the taper had a length of straight tubingextending from it. The tube has a starting gauge of 14 gauge.

The swaging method of the present invention was used to create, in onepass, a taper having a taper angle which exceeded 12 degrees. The taperhad a starting diameter of 2.500 inches, a small diameter of 1.610inches, and a taper length 26.910 inches. The tube has a starting gaugeof 16 gauge.

1) A method for imparting a taper of length greater than 12 inches to atubular metal work piece, said method comprising the steps of: a)providing a tubular metal work piece; b) providing a rotary swagingmachine comprising a die comprising: a die taper of length greater than12 inches; a die taper having a reduction in diameter of greater thanabout 30%; or a die taper having a taper angle of greater than about 12degrees; c) rotary swaging an endlength of said tubular metal workpiece, with said rotary swaging machine, through said die, therebyimparting a taper to the work piece; wherein the taper imparted to thework piece in a single pass has a length bounded by a first diameter anda second diameter; wherein the second diameter is less than the firstdiameter; and wherein the taper is free of flaking and cracks. 2) Amethod as in claim 1 wherein the die has the following specifications:a) a first diameter in the range of from about 2.5 to about 6.0 inches;b) a smallest diameter in the range of from about 0.5 to about 2.5inches; and c) a taper length of greater than about 12 inches. 3) Amethod as in claim 1 wherein the tubular metal work piece provided in a)has a diameter less than or equal to the first diameter. 4) A method asin claim 3 wherein upon completion of step c), the tubular metal workpiece has a smallest diameter equal to the diameter of the narrow borediameter. 5) A method as in claim 1 wherein the die comprises 2, 3 or 4die elements. 6) A method as in claim 1 wherein in step c), the workpiece is fed into the rotary swaging machine at a rate in the range offrom 0.062 to 0.500 inches per second. 7) A method as in claim 1 whereinthe workpiece rotates at a speed of 40-60 rpm. 8) A method as in claim 1wherein the die comprises a die taper of length greater than 12 inchesand a die taper having a reduction in diameter of greater than about30%. 9) A method as in claim 1 wherein the die comprises a die taper oflength greater than 12 inches and a die taper having a taper angle ofgreater than about 12 degrees. 10) A method as in claim 1 wherein thedie comprises a die taper having a reduction in diameter of greater thanabout 30% and a die taper having a taper angle of greater than about 12degrees. 11) A tubular metal work piece tapered by the method of claim1, and additionally comprising a length of constant diameter tubingextending from the small diameter end. 12) A tubular metal work piece asin claim 11 wherein the taper profile comprises at least one convexregion. 13) A tubular metal work piece as in claim 11 wherein the taperprofile comprises at least one concave region. 14) A die element havingthe following specifications: a die taper of length greater than 12inches; a die taper having a reduction in diameter of greater than about30%; or a die taper having a taper angle of greater than about 12degrees. 15) A die element as in claim 14 wherein the die comprises adie taper of length greater than 12 inches and a die taper having areduction in diameter of greater than about 30%. 16) A die element as inclaim 14 wherein the die comprises a die taper of length greater than 12inches and a die taper having a taper angle of greater than about 12degrees. 17) A element die as in claim 14 wherein the die comprises adie taper having a reduction in diameter of greater than about 30% and adie taper having a taper angle of greater than about 12 degrees. 18) Adie as in claim 14 wherein the taper profile is linear. 19) A die as inclaim 14 wherein the taper profile comprises at least one convex region.20) A die as in claim 14 wherein the taper profile comprises at leastone concave region.